The invention relates in general to the field of beamforming techniques. In particular, it concerns apparatuses and methods for beamforming signals or computing beamformed signals, by explicitly targeting designed regions of interest.
Wifi networks in general are often perceived as being rather inefficient, inasmuch as signal goes where it is not necessarily needed, while dead zones may occur where the signal barely reaches. Moreover, rather than being equally distributed around or away from a router, end devices tend to get more and more mobile, i.e., they move around the routers with increasing vigor as users, e.g., walk with their smartphone or tablet, at home or in public networks.
Newer Wifi standards, 802.11n and more recently 802.11ac, provide improvements, wherein multiple antennas are deployed and the location of devices can be detected (either passively or with help of explicit status communication) so as to use multiple-input and multiple-output methods, or MIMO, which involve beamforming. The effect is some increased network capacity, and a level of concentration of energy to where it is needed.
Mobile phone networks (3G, 4G, and in the future 5G), have similar issues over a wider area, though engineered for far more devices per transmitter. Such network must, by definition, cope with people moving (walking, running, or in a vehicle). The problem is made even more complicated than in the Wifi case due to variability in elevation. In order to beamform, ever increasing numbers of antennas per mast are deployed. Given the number of devices, it is impossible to even contemplate focusing beams on any single device/user.
Besides, beamforming is an intrinsic part of modern ultrasound. An ultrasound probe is essentially an array of transducers, responsible for both transmitting sound waves, and receiving the resultant echoes. Transmit beamforming cleverly plays with the timing of the sound pulse sent from each transducer, so as to induce constructive wave interference and aim at focusing at a certain angle into the body or object to a desired depth. The resultant echoes are then picked up by the transducers, and digitally beamformed, so as to target the echo signals to focus on the same desired depth and angle.
In yet another technical field, modern large-scale radio telescope arrays use massive numbers of antennas, i.e., tens of thousands, with up to the order of a million for the future Square Kilometer Array. The shear volume of data makes it neither feasible to transmit it to a central location nor to correlate the outputs of each pair of antennas. Thus, beamforming is deployed on groups of antennas primarily as a method for data reduction, but also in an attempt to focus on a single part of the sky.
In the prior art, there are advantages of implementing a Minimum variance distortionless response (MVDR) beamformer in ultrasound, as opposed to the standard focused beamformer (here called delay-and-sum). MVDR beamforming seeks to achieve focused beamforming by adapting its weights based on the signal to be beamformed. Focused beamforming for ultrasound in a compressed fashion my be achieved.
Previous beamforming techniques are perceived to lack flexibility. Some attempts for filtering in a discrete manner have been made, but the proposed techniques are perceived to be either too restrictive in array layout, or involve ill-posed optimization problems that could result in beamforming coefficients with very large moduli, and hence an unreliable beamshape.